In the process of manufacturing a semiconductor device, the introduction of impurities (dopant) is a step required for forming a p-n junction in a semiconductor wafer. Currently, impurities are generally introduced by ion implantation and subsequent annealing. Ion implantation is a technique of ionizing elements of impurities such as boron (B), arsenic (As), or phosphorous (P) to collide the ions with a silicon semiconductor substrate at high acceleration voltage, thereby physically implanting impurities (for example, see Patent Document 1). The implanted impurities are activated through annealing.
Traditionally performed ion implantation has an advantage of easily controlling the implantation depth and concentration of impurities in the introduction of impurities. The increasingly smaller sizes of semiconductor devices, however, require the introduction of impurities in only an extremely shallow region (with a depth not greater than several nm) of a surface layer of the substrate. Ion implantation has difficulty in implanting impurities in only such an extremely shallow surface layer region. The 3D transistor technology, which has been under development, needs to introduce impurities into a concavo-convex three-dimensional pattern. It is therefore difficult to uniformly introduce impurities into the entire surface of the concavo-convex pattern by ion implantation of colliding ions from one direction.
Under the circumstances, the following technique has been researched, which supplies a dopant-containing chemical solution to the surface of the silicon substrate by a wet treatment and diffuses the dopant in a substrate surface layer by a subsequent heat treatment, thereby introducing impurities into only an extremely shallow region of the substrate surface layer (see Non-Patent Document 1). In the technique disclosed in Non-Patent Document 1, a native oxide film is removed from the surface of the silicon substrate with a dilute hydrofluoric acid, the hydrogen termination treatment is then performed to stabilize the surface state, and then, a dopant-containing chemical solution is supplied to the hydrogen-terminated substrate surface. Such a combination of the wet treatment and the thermal diffusion allows the introduction of impurities into only an extremely shallow region of the surface layer of the substrate, and also allows impurities to be uniformly introduced into the entire surface of a complex concavo-convex pattern.